Overheating safety system for electric discharge tubes



Aug. 29, 1950 2,520,476

H. l. STANBACK OVERHEATING SAFETY SYSTEM FOR ELECTRIC'DISCHARGE TUBES Filed March '2, 1949 Patented Aug. 29, 1950 UNITED STATES OFFICE OVERHEATIN G SAFETY SYSTEM FOR ELECTRIC DISCHARGE TUBES tion of ldichigan I Application March 2, 1949; Serial No. 79,211

8 Claims.

This invention relates to safety systems-preventing overheating of electricdischarge tubes.

Electric discharge tubes of themercury pool cathode type controlling translating circuits carry large currents and means must be provided for carrying away the heat'caused by'thesezcurrents or the tubes will be destroyed. It:.is the practice to circulate coolingwater 'around 'the tubes to cool them to safe temperatures, .and to provide a water-flow switch sensitive to the temperature of the water. leaving the-.tubesrand capable of interrupting the electric control icircuit in case the temperature ofthat water becomes too high,- the high temperature indicating improper cooling of the power tube. One'eform of such switch comprises a; metal block or pipe through which the cooling water flows, the pipe or block being heated by electricity, and this :heat also being carried awayby the cooling water. 'If the water flow stops or if flow is so impeded that the power tubes are not properly cooled, the pipe or block becomes overheated and a bimetallic strip subject to pipe temperature. flexes to open the control circuit-and thus acts to stopallcurrent flow through the discharge tube by preventing its becoming conducting. Themetal block or pipe through'which the cooling water fiowsis heated by means of a resistance winding connected to the power source; When this winding burned out, or heating current otherwise failed to flow therethrough in the past, the pipe or block which it normally heated would be-cool and the bimetallic member would not be heated. sufficiently to interrupt'the tube control circuit even though the temperature of the cooling water indicated dangerous operating temperature within the discharge tube. In such'cases, theexpensive discharge tubes were frequently destroyed.

Therefore, one object of this invention is to protect the electric'dlscharge tubes in the event of burn-out of the heater of afiow switch; the switch being responsive to the temperature of the water which serves to cool the discharge tubes.

Another object of the present invention'is to provide a safety system protecting electric discharge tubes against overheatingin which power flow-through the tubesis interruptedupon the occurrence of burn-out of,'short'circuit through, or local power failure to; theheating coil of a flow switch responsive to cooling water temperature.

Another object is to provide a safety system in accordance with the preceding objects inwhich burnout of, or local power failure to, the: heater coil prevents conduction oian' electric valve inthe 55 rectifier tube 1 8.

Other objects and features: of. the invention will be readily apparent to those skilledsin-the art from the specification and appended 1 drawing illustrating 1 certain preferred embodiments "in which the figure is adiagrammaticalrepresentationzof a circuit including the safety system 'of this invention.

2 The invention as illustrated in the single figure of the, drawing employs a source of. alternating voltage connected: to conductors l serving to sup- 5 ply power to control and load circuitsl Transformer 2 has its primaryenergized by the source and has an initiating switch 3 controlling a circuitbypassing the transformer 2 primary. I The secondary voltageof transformer 2, modified as hereinafter explained, is applied tojthe grid 4=of electric .valve 5. The secondary of transformer 2 charges capacitor 1 bygrid rectification of'valve 5. 'I'hisaction'rproduces a hold-off biasat grid 4 of valve 5 equal "to the output of transformer 2 displaced from the cathode potential of'valve 5 by the amount of then C-VOlliQflG ElCIOSS capacitor I. The secondary of transformer 1- also chargescapacitor 8 through rectifier 9 to'produce thereon a D. O. voltage. This voltageopposes a sawtooth voltage across capacitor ll produced by the output of transformer 6 through rectifier'lZ and by the rapid discharge of "capacitorll through resistor is during periods of non-conduction of rectifier I2. The resultant'of'the opposingvoltages-of capacitor 8 and capacitor H" is applied to the grid 4 of valve 5 through a. resistor l4which'alsoserves as a bleeder for-capacitor I.

There isprovided a transformer is having its primaryconnected to the supply acrossthe lines land its'secondary connected to the anode and cathode of valve 5 through'the rectifier tube 18 and the parallel circuit formedby the timing capacitors I5 and I 6. Bypassing-the capacitor I5-is anradjustable resistor 22 and bypassing the capacitor 16- is a resistor 2| having an intermediateetapmfipoint initially adjustable and normally set in the operation of the system.

'A. transformer 23 has its primary connected to the-supply across lines I and its secondary output fed to the anode 24 and cathode .26 of the electric valve 25 throughthe primaryof transformer 29. The control grid 21 of valve 25' is-connectedtothe tap-ofifipoint of resistor 2| and'the'cathode 26 is connectedbetween the capacitor l5 and the The secondary 0f the transformer 29 is connected across the capacitor 34' connected in the circuit of the grid 35 of electric valve 3| which controls the charging of the firing capacitor 36.

A transformer 32 has its primary energized from the supply across lines I and its secondary in the circuit of grid 35 in series with the capacitor 34 and a capacitor 33 bypassed by resistor 30. The anode and cathode of the valve 3| are connected across the secondary output of a transformer 20 in series with a firing capacitor 35. The primary of transformer 25 is energized from the supply across lines I. Also in series with the anode circuit of the valve 3| are the contacts 65 of a thermal flow switch for the electric discharge tubes 48 and 45 and the primary of a transformer 31. Across the firing capacitor 36, which discharges therethrough, are connected the igniter 51 and mercury pool cathode 58 of electric discharge tube 45 through an electric valve 43. Valve 43 has its grid connected to a hold-off bias circuit comprising the secondary of transformer 39 and capacitor 4| bypassed by resistor 42, the primary of transformer 39 being connected to the supply across lines I.

Connected back to back with the electric discharge tube 40 is a second tube 45, these discharge tubes serving to pass both half cycles of supply current through the load represented by the welding transformer 66 supplying a welding load at 44. Electric discharge tube 45 is fired by components similar to those set forth with respect to tube 49, these constituting the firing capacitor 52, the discharge valve 45 and charging valve 38.

To secure proper firing of the charging valve 38, the secondary output of transformer 31 is fed across a capacitor 41 in the grid circuit of valve 38, in series with the elements supplying the hold-off bias and constituted by the secondary of transformer 5| and the capacitor 48 bypassed by resistor 49. The capacitor 41 is bypassed by the discharge resistor 6|. In series with the firing capacitor 52 and the valve 38 are the contacts 32 of the thermal fiow switch.

The heaters for the thermal fiow switches, whose contacts are shown at 6|! and 62, are shown at 55 connected in series with each other and through the primary of transformer 54 to a tap-ofi point of an auto transformer 53 connected across lines I. The secondary output of transformer 54 is fed through the cathode heaters or filaments of the rectifier tube [8.

In the drawing, the surge bypass capacitor for the electric valves have been shown but they have not been described; the grid resistors and cathode heaters which would be used have been neither shown nor described as these are conventional elements not essential to the invention, although they would customarily be used in a working circuit.

The operation of the discharge tube control system is as follows:

When initiating switch 3 is closed, the output voltage of transformer 2 disappears and capacitor 1 discharges rapidly. The voltage at control grid 4 of electric valve 5 quickly changes, therefore, from the near sine wave curveof capacitor 1, consisting of the D. C. voltage due to grid rectification plus the A. C. output of transformer 2, to the sawtooth voltage of capacitor plus the steady D. C. voltage of capacitor 8. Valve 5 fires at the next sawtooth peak grid voltage after closure of the initiating switch 3. Valve 5 ceases to conduct as soon as timing capacitors I5 and I6 are charged, capacitor 8 being rapidly discharged through resistor IT. This leaves at the grid 4 of valve 5 only the capacitor sawtooth voltage which is always sufficiently negative to prevent conduction of valve 5, which will, therefore, conduct for only a portion of a half cycle for each closure of the initiating switch 3.

While valve 5 conducts, capacitors I5 and I6 are charged through rectifier tube l8, said capacitors being charged at the same time from the same voltage source, both charging circuits having the same impedances. Therefore, capacitors l5 and I5 are charged to the same voltage and then effectively disconnected from the supply transformer l9 as valve 5 ceases to conduct. Capacitor i6 discharges very slowly through the voltage dividing resistor 2|; capacitor l5 discharges more quickly through the weld time adjustment resistor 22.

Transformer 23 is so disposed as to make the anode 24 of valve 25 negative with respect to cathode 26 during the period of conduction of '25 and will remain so until capacitors l5 and I5 discharge to the cross-over point, where the potential of capacitor I5 is equal to that at the tap on the capacitor-bridging resistor 2| and subsequent positive potentials of the anode 24 with respect to cathode 26 will not fire the valve 25. Time measuring valve 25 will conduct, therefore, on the next half cycle after valve 5 and tube l8 conduct and will continue to con duct during each half cycle during which anode 24 is sufficiently positive with respect to cathode 26 until the above mentioned cross-over point is reached. Conduction of valve 25 energizes coupling transformer 29 which delivers to the grid circuit of valve 3| a measured number of pulses equal in number to the number of full cycles of weld time desired.

Grid 35 of charging valve 3| receives A. C. hold-off voltage from transformer 32 output plus a D. C. component across capacitor 33 which is charged by valve 3| grid rectification. Each output pulse from coupling transformer 29 charges energy into capacitor 34. This energy is discharged into the circuit of grid 35 at the beginning of the following half cycle, providing a voltage signal which overcomes the hold-off bias on grid 35 and causes valve 3| to conduct.

Conduction of valve 3| charges firing capacitor 36 through current transformer 31. Each time capacitor 36 is charged, valve 3| conduction current energizes transformer 31 and the output from the secondary of transformer 31 delivers a, pulse to the valve 38 grid circuit.

, The circuit consisting of grid bias transformer 39, capacitor 4| and resistor 42 provides D. C. hold-off voltage for valve 43. After the firing capacitor 36 is charged, the tube 43 fires as its grid voltage becomes less negative and quickly discharges capacitor 38 through resistor 50, inductor38, the igniter 51 and mercury cathode pool :58 of discharge tube 40. Resistor 59 and inductor 3B serve to shape the discharge pulse of capacitor 36 for best firing performance, the

high current, p lse prcducediby theadiseharee se ving to initiate -toonduc ien: QitflbfiAQ in conventional manner.

. Discharge tubes ft and -45-accornplish= the function of switching the. primary .currentto. the wider transformer 66, being connected, ba k to backin serieswith onepower line to the welder transformer and serving in-,effect.- as a single. pole eontactor.

The-circuits for valves '38., 46 and tube are substantially. the. same s the previously described circuits for valves. iii, 43 and tube Atrcspecti-va 1y. Valve 38 fires in response totheoutput pulses of transfQrmer 31 .whicnoccur each time-valve til-conducts. Each of these pulses c argesener y into capacitor 41, this energy being: discharged intothe grid circuit of valve 38 at, thebeginning of. the following half cycle; providin a; voltage peak. which overaorrresthe-hold-ofi bias due to capacitor 48, resistor 49, and transformer L When va1ve38 fires, it charges firing capacitor 52..the firing capacitor bein discha dby con duction of valve .45, to effect conduction of meroury pool. tube .45 in the same manner as previously describedfor the interaction of capacitor-3 valve43, endmercury pool tube All.

Transformer 54- isseen to have its secondary in series.withthefilamentbfi of relatively. me pensive rectifier tubelfi and its primary :inseries with the thermal flow-switch heaters 55.. The transformer ratio issoselected that in, normal operation the flow switch current throughthe primarytransforms'to. proper filament current in the secondary. The supply voltage tap on transformer 53,-is selectedso that both heaters and tube filament receive proper voltage. In the event one or both of the thermal flow switch heaters 55 should burn out, the associated thermal flow switch becomes inoperative to protect the discharge tubes with which it is associated. Upon the occurrence of such burnout, the primary circuit of transformer 54 is interrupted so that current ceases to flow through the filament 56 and the tube l8 becomes non-conducting to prevent further charging of the timing capacitors I5 and I6 and thus interrupt further conduction through the discharge tubes after the completion of any timin cycle in operation at the time of burnout. In the event of local power failure, current again ceases to flow through the filament 56 and the tube I8 is nonconducting to prevent further timing of a conducting cycle for the discharge tubes.

Upon the occurrence of a short circuit through one or both of the thermal flow switch heating resistors 55, the current through the primary of transformer 54 will be greatly increased and the secondary current flowing through filament 56 will be sufficiently high as to burn out the filament to render the tube I8 non-conducting. The rectifier tube I8 is relatively inexpensive compared to the discharge tubes and serves to protect the discharge tube without the necessity of fusin and other complications in the circuit.

It will readily appear, therefore, that the expensive discharge tubes in the circuit are protected from any type of failure of the thermal flow switch heaters and that no harm can be sustained by the electric discharge tubes due to any of the faults to which said thermal flow switch heaters are normally subject.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto, as many variations will be readly apparent those skilled in theart and the invention is to be given its broadest possible interpretation within the termsof the following claims.

whatisclaimedis:

1.:-,In a-csafety system for thermal flow switch overheating. protection for electric discharge tubes-an. electric discharge tube for controlling the passage lOfl' current to a load, means including an electronictube controlling the conduction oil-said electric discharge tube, a thermal flow switch "including cooperating contacts and a heater, a transformer, means connecting the primary of saidtransformer in series with said heater, and. means connecting the secondary of saidtransformer to the cathode heater of said electronictube, said electronic tube bein of the type requiring a hotcathode for conduction and preventing conduction of the electric discharge tubeuuponfailu-re :of current flow through the thermal flow-switchheater.

. 2.:In asafety system for thermal flow switch overheating protection for electric discharge tubes; an electric discharge tube for controlling the passage-of current to a load, means including anelectronic' tube controlling the conduction ofsaid electric discharge tube, a thermal flow switch including. cooperating contacts and a heater and-means supplying energy to the oathode. heaterofsaid electronic tube, said last mentioned meansrbeing. responsive to current flow through said thermal flow switch heaters, said electric valve being of theztype requiring a hot cathode for. conduction and preventing conduction :ofthe-eleotric discharge tube upon failure elf-current flowthrough, or short circuit of, said thermal flow switch heaters.

3. In a safety system for thermal flow switch overheating protection for electric discharge tubes, an electric discharge tube for controlling the passage of current to a load, means including an electronic tube controlling the conduction of said electric discharge tube, a thermal flow switch including cooperating contacts and a heater, a transformer, means connecting the primary of said transformer in series with said heater, means connecting the secondary of said transformer to the cathode heater of said electronic tube, said electronic tube being of the type requiring a hot cathode for conduction, said cathode heater burning out and preventing conduction of the electric discharge tube upon the occurrence of a short circuit of said thermal flow switch heater.

4. In a safety system for thermal flow switch overheating protection for electric discharge tubes, an electric discharge tube for controlling the passage of current to a load, means includling an electronic tube controlling the conduction of said electric discharge tube, a thermal flow switch including cooperating contacts and a heater, a transformer, means connecting the primary of said transformer in series with said heater, means connecting the secondary of said transformer to the cathode heater of said electronic tube, said electronic tube being of the type requiring a hot cathode for conduction and preventing conduction of the electric discharge tube in the event said thermal flow switch heator should be deenergized or short circuited.

5. In a. safety system for thermal flow switch overheating protection for electric discharge tubes, an electric discharge tube for controlling the passage of current to a .load, means controlling the timing of conduction of said discharge tube, other means including an electronic tube controlling the initiation of operation of said timing means, a thermal flow switch including cooperating contacts and a heater, a transformer, means connecting the primary of said transformer in series with said heaters, means connecting the secondary of said transformer to the cathode heater of said electronic tube, said electronic tube being of the type requiring a hot cathode for conduction and preventing initiation of operation of said timing means upon failure of current flow through the thermal flow switch heater.

6. In a safety system for thermal flow switch overheating protection for electric discharge tubes, an electric discharge tube for controlling the passage of current to a load, timing means controlling the period during which said discharge tube conducts, other means including an electronic tube controlling the initiation of operation of said timing means, a thermal flow switch including cooperating contacts and a heater, a transformer, means connecting the primary of said transformer in series with said heater, means connecting the secondary of said transformer to the cathode heater of said electronic tube, said electronic tube being of the type requiring a hot cathode for conduction'and preventing the initiation of a period in which said electric discharge tube could conduct should said thermal flow switch heater be deenergized or short circuited.

'7. In a safety system for thermal flow switch overheating .protection for electric discharge tubes, an electric discharge tube for controlling the passage of current to a load, timing means controlling the period during which said discharge tube conducts comprising resistors and capacitors of different decaying rates, means including an electronic tube controlling the admission of charge to said capacitors, a thermal flow switch including cooperating contacts and a heater, a transformer, means connecting the secondary of said transformer to the cathode heater of said electronic tube, said electronic tube being of the type requiring a hot cathode for conduction and preventing the initiation of a period in which said electric discharge tube conducts when said cathode heater is deenergized.

8. In a safety system for thermal flow switch overheating protection for electric discharge tubes, an electric discharge tube for controlling the passage of current to a load, timing means controlling the period during which said discharge tube conducts, means including an electronic tube controlling the initiation of operation of said timing means, a thermal flow switch including cooperating contacts and a heater, means supplying energy to thecathode heater of said electronic tube, said last mentioned means being responsive to current'fiow through said thermal flow switch heater, said electronic tube being of the type requiring a hot cathode for conduction and preventing the initiation of a period in which said electric discharge tube conducts upon failure of current flow through, or short circuit of, said thermal flow switch heater.

' HARRIS I. STANBACK.

No references cited. 

